Imidazole Encapsulation In Metal Organic Framework Material MOF-5and Its Proton Conductivity

Metal organic frameworks are a new type of porous materials, characterizedby regular pores, high thermal stability, tunable pore structure and pore sizes, andthey haves howed a variety of potential applications, such as gas storage, gasseparations, sensors and luminescent materials. In this paper，we synthesised theporous metal-organic framework material MOF-5by the self-assembly of zinc ionsand terephthalic acid ligands, then proton carrier imidazole was loaded into thepores of MOF-5. MOF-5and MOF-5loaded with imidazole were characterized bypowder X-ray diffraction （PXRD）, scanning electron microscopy （SEM）, etc; andthe thermal stability of MOF-5and MOF-5loaded with imidazole were studied bythermal gravimetric analysis （TG）. Conductivity of MOF-5loaded with imidazolewas measured by A.C impedance at various temperatures.MOF-5with high stability, simple structure and regular pores was synthesizedby solvothermal method in this paper. The effects of reaction temperature, reactiontime, the molar ratio of the reactants and the treatment methods on the MOF-5synthesis were studied. The experiment results showed that the MOF-5with highquality was obtained at synthesis condition of Zn（NO₃）₂·6H₂O/H₂BDC=2:1（mol/mol）,24h reaction time,15mL DMF and the reaction temperature is120℃or135℃. In the post-treatment of synthesized MOF-5, the guests can befully removed by both chloroform extraction and temperature activation methods.Imidazole was loaded into the pores of MOF-5by the means of liquid method,and the composite of imidazole-loaded MOF-5was prepared. The effects of solvent,heat temperature and the mass of imidazole on the process of encapsulation hadbeen investigated. XRD and SEM analysis showed that the structure and images ofMOF-5were not destroyed after the encapsulation of imidazole. The TG resultshowed that the thermal stability of composite of imidazole-loaded MOF-5has notbeen changed after the encapsulation of imidazole, but the imidazole in the pores ofMOF-5began desorption when the temperature was above130℃. Conductivity ofMOF-5loaded with imidazole was measured by A.C impedance spectroscopy. Theresult indicated that the proton conductivity of composite of imidazole-loadedMOF-5increased as the increasing of temperature between room temperature and120℃, but the proton conductivity composite of imidazole-loaded MOF-5decreased when temperature above140℃.. The ptoton conductivity of compositeof imidazole-loaded MOF-5is3.5×10^-8S/cm at120℃，which is about threeorders of magnitude higher than that of the pure MOF-5.